Shiva and Shakti

The Tantrics call the Self-creative Power of the Supreme Absolute Shakti (usually transliterated as "S'akti"), from the Sanskrit root S'ak, "to
be able, to have force to do, to act" [Arthur Avalon, Shakti and Shakta, Dover books, p. ].

Without Shakti, there is no Creation. As the Bengali Shakta Tantrics
are fond of saying: "Shiva (the Absolute Consciousness-Being) without Shakti
is a corpse" (i.e. lifeless, inert). Hence there must also be a Power
of manifestation. This is Shakti.

So the Absolute Reality is made up of two fundamental principles: Shiva,
the Absolute in its own essential, perfect, unchanging, non-dual Consciousness,
nature; and Shakti, which is that Absolute's own Power of self-manifestation.
As Jaideva Singh explains, "Shakti is nothing separate from Shiva,
but is Shiva Himself in His creative aspect" [p.9].

Shiva is nivritti (state of rest) and Shakti is pravritti (state of
activity), in the ultimate state they remain in a union of oneness.
This is the principle of non-duality (advaya) which is described
in the Tantric texts in terms of maithuma (sexual intercourse) or kama-kala
("unit of desire"). One text, the Kama-kala-vilasa describes
Shiva or Mahesha as pure illumination or self-shining (prakasha-matra-tanu)
with all the principles of activity contracted within it. Shakti
the seed of the future world (bhavi-chachara-bijam). Shiva realises
himself through Shakti, reflection [Shashibhusan Dasgupta, Obscure Religious
Cults, p.333 (1969 Firma KLM Private Ltd, Calcutta)]